The present invention relates to a capacitor and a method for fabricating the same, and a semiconductor device including the capacitor.
Conventionally, capacitors have been formed in a semiconductor device, such as memory devices, DRAM, FRAM, etc., RF devices, analogue devices or logic devices, etc.
The capacitors comprise lower electrodes, a capacitor dielectric film formed on the lower electrodes, and upper electrodes formed on the capacitor dielectric film.
Capacitors using as materials of the lower electrodes and the upper electrodes semiconductors, such as polysilicon, amorphous silicon, etc. are called capacitors of SIS (Silicon Insulator Silicon) structure.
Capacitors using semiconductors as materials of the lower electrodes and metals as materials of the upper electrodes are called capacitors of SIM (Silicon Insulator Metal) structure.
The capacitors of SIS structure and the capacitors of MIS structure use semiconductors, such as polysilicon, etc. in at least the lower electrodes, and the electric resistance of the electrodes are relatively high. The capacitors cannot have good high-speed response.
Then, recently capacitors of MIM (Metal Insulation Metal) structure using metals as materials of the lower electrodes and the upper electrodes are proposed. The capacitors of MIM structure use metals both in the lower and the upper electrodes, and accordingly, the lower electrodes and the upper electrodes have low electric resistances. The capacitors can have good high-speed response.
To form capacitors having good electric characteristics, after the lower electrodes and the capacitor dielectric films have been formed, heat processing of a temperature of above 650° C. at lowest must be performed for improving film quality of the capacitor dielectric films. Improved film quality of the capacitor dielectric film is very important to improve voltage resistance of the capacitors and decrease leak current. As metals which can bear the high-temperature heat processing are considered W (tungsten), WN, TiN, Ru, RuO, etc. These materials have relatively high resistivities. Specifically, the resistivity of W is about 6-9 μΩ·cm, the resistivity of WN is about 50 μΩ·cm, the resistivity of TiN is about 50 μΩ·cm, the resistivity of Ru is about 10-15 μΩ·cm, and the resistivity of RuO is about 140 μΩ·cm. On the other hand, Al, which has a low resistivity of 2.7 μΩ·cm but has a low melting point of 630° C., cannot unusably withstand the high-temperature heat processing described above. Accordingly, it has been conventionally impossible to form the capacitors of good high-speed response by using materials of low resistivities, such as Al, as materials of the lower electrodes.
When the heat processing for improving film quality of the capacitor dielectric film is performed after the lower electrodes and the capacitor dielectric film which are formed of metals, there is a risk that the lower electrodes will deprive oxygen from the capacitor dielectric film to resultantly deteriorate, to the contrary, film quality of the capacitor dielectric film.
The fabrication process of semiconductor devices is divided largely in bulk steps and layer steps. In the bulk steps, heat processing of high temperatures of about 1000° C. are performed, and when metal electrodes are formed in a bulk step, there is a risk of metal contamination. Accordingly, the metal electrodes cannot be formed in a bulk steps. Thus, the capacitors using the metal electrodes cannot be formed on a layer to be formed in a bulk step.